1. Field of the Invention
This invention relates to injecting a micellar system into a subterranean formation and displacing it toward a production means to recover hydrocarbon therethrough. The micellar system is comprised of crude oil sulfonates.
2. Prior Art
Micellar dispersions are useful for recovering crude oil from subterranean formations; for example, see U.S. Pat. Nos. 3,254,714; 3,275,075; 3,506,070; 3,497,006; 3,613,786; 3,734,185; 3,740,343; 3,827,496; 3,964,548; and 3,827,496. The prior art generally teaches that the micellar dispersion is injected into the formation followed by a mobility buffer fluid and thereafter drive water to displace the previously injected fluids toward the production well. Pre-slugs can be injected before the micellar dispersion.
Injectivity of the micellar dispersion and other fluids used in the recovery process have always been of concern. It is desirable to have a high injectivity index to reduce the surface energy required for and to improve the displacement efficiency of the flooding process. Generally speaking, the amount of oil that can be recovered from the reservoir is directly dependent on the amount of fluid that can be injected into and displaced through the reservoir, discounting physical properties of the fluid, etc. Waxes have been and continue to cause major injectivity problems.
Examples of references relating to the extraction of wax are as follows:
British Pat. No. 134,215 (Nash et al.) teaches reduction of the wax content of mineral oils by contacting the mineral oil with a solvent, e.g. aliphatic monohydric alcohols, at a temperature above the melting point of the wax and thereafter cooling the solution to precipitate the wax. The solvents must be miscible with the wax-free mineral oil.
U.S. Pat. No. 2,063,369 (Diggs et al.) teaches extracting wax from wax-bearing oil by thoroughly mixing the oil with 1.5-2 volumes of dichloroethyl ether, then heating the mixture to 145.degree.-170.degree. F. and thereafter permitting it to settle.
U.S. Pat. No. 2,149,574 (Brown) teaches extracting wax from oils using chlorophenol.
U.S. Pat. No. 2,202,389 (Lewis et al.) teaches extracting hydrocarbon by contacting a hydrocarbon mixture with a light hydrocarbon containing 1-8 carbon atoms at a temperature between 38.degree. C. and the critical temperature of the light hydrocarbon solvent, thereafter maintaining the mixture at a sufficient pressure to retain the light hydrocarbon solvent in the liquid phase whereupon two phases form.
U.S. Pat. No. 2,698,279 (Mondria) teaches extracting wax from mineral oils using a dewaxing solvent such as halogenated hydrocarbons; aliphatic and aromatic hydrocarbons such as petroleum ether, petroleum naphtha, gasoline, hexane, benezene, etc.; ketones; etc.
U.S. Pat. No. 3,302,713 (Ahearn et al.) teaches dewaxing petroleum distillates and then sulfonating them to obtain sulfonates desirable for flooding subterranean formations.
Liquid extraction of wax from crude oil is also taught in the Oil and Gas Journal, Dec. 12, 1929, Page 125, and British Pat. Nos. 149,347; 507,646; and 534,212. Examples of extraction solvents in the Oil and Gas Journal are ethyl, butyl, and amyl acetates, kerosene, etc.
Injection of micellar dispersions containing crude oil sulfonates is a particularly current problem. During injection the micellar system is cooled as it is transported from the surface facility to the well head. It is partially reheated as it is transported from the well head down to the sand face of the subterranean formation. Some of the insoluble wax crystals that form during cooling are not redissolved with the partial reheating and/or do not immediately go back into solution. These wax crystals tend to "block" or "plug" the reservoir rock as the micellar dispersion is being injected. This adverse effect is apparent even if the micellar dispersion has been filtered at high or low temperatures prior to injection. U.S. Pat. No. 3,951,828 teaches a solution to the problem by incorporating 0.01-10 percent by weight of a low molecular weight paraffinic hydrocarbon into the micellar dispersion. However, with this technology, the micellar dispersion must be subjected to a "fast cool-down rate" -- i.e., greater than about 1.degree. C./min in the 5.degree.-15.degree. C. wax crystalization range. The hydrocarbon keeps the lower molecular weight waxes which would form large "plate" or "needle" type crystals during cooling in solution and prevents reservoir plugging. The higher molecular weight waxes form very small mal type crystals which do not plug the reservoir. A description of wax crystal types can be found in Clarke, E. W., "Crystal Types of Pure Hydrocarbons in the Paraffin Wax Range", Industrial and Engineering Chemistry, Volume 43, Page 2526 (1951) and Ferris, S. W. and Cowles, H. C., "Crystal Behavior of Paraffin Wax", Industrial and Engineering Chemistry, Volume 37, Page 1054 (1945). However, when micellar systems are subjected to a "slow cool-down rate" -- i.e., less than about 0.7.degree. C./min in the 5.degree.-15.degree. C. range, the mal crystals formed are sufficiently large to cause reservoir plugging. Both types of cool-down rates can occur in various oil field applications.